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How Populations Evolve Quirós Araya Daniela 10A, . - Coggle Diagram
How Populations Evolve
Quirós Araya Daniela 10A
15.1 > How Are Populations, Genes, and Evolution Related?
Genes and the Environment Interact to Determine Traits
A gene is a segment of DNA located at a particular place on a chromosome.
At a given genes location, different members of a species may have different nucleotide sequences called alleles. They can influence eye color.
Homozygous: individual of a diploid species whose alleles of a particular gene are both the same.
Heterozygous: different alleles for that gene.
Specific allele borne on organisms chromosome (genotype) interact with environment to influence the development of its physical and behavioral traits (phenotype).
Evolution is a property of populations. Population is a group that includes all the members of a species living in a given area.
The Gene Pool Comprises All of the Alleles in a Population
Population genetics deal with frequency, distribution and inheritance of alleles in populations.
Population genetics define a gene pool as a set that contains all of the alleles of all of the genes from all of the individuals in a population.
A gene pool is not an actual physical entity but is instead a mental construct that can help us understand the process of evolution.
Each partícula gene can be considered to have its own gene pool, which compromises all od the alleles of that specific gene in a population.
An alleles proportion in the gene pool is its allele frequency.
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Evolution Is the Change of Allele Frequencies Within a Population
Evolution is change in the genetic makeup of populations over generations.
A population geneticist defines evolution as changes over time in the allele frequencies of a gene pool.
Outward changes that we observe in individuals can be viewed as visible expression of underlying changes to the gene pool.
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The Equilibrium Population Is a Hypothetical Population in Which Evolution Does Not Occur
Equilibrium population: non-evolving population in which allele frequencies do not change.
Conditions
No mutation
No gene flow
Large population
All mating must be random
No natural selection
If one or more of these conditions are violated, population will evolve.
This conditions are useful starting points for studying the mechanisms of evolution.
Godfrey H. Hardy & Wilhelm Weinberg: Hardy-Weinberg principle. Under certain conditions, allele frequencies and genotype frequencies in a population will remain constant no matter how many generations pass (population will not evolve).
15.2 > What Causes Evolution?
Mutations Are the Original Source of Genetic Variability
Inherited mutations are rare but important: without mutations, there would be no evolution.
Mutations are not goal directed: a mutations simply happens and may produce a change in a structure or function of the organism that depends on environmental conditions.
Gene Flow Between Populations Changes Alleles Frequencies
Gene flow: movement of alleles between populations that changes how alleles are distributed among populations
The main evolutionary effect of gene flow is to increase the genetic similarity of different populations of a species.
If alleles move continually back and forth between different populations, the gene pools of the different populations will mix.
If gene flow between populations of species is blocked, resulting genetic differences may grow so large that one of the populations become a new species.
Allele Frequencies May Change by Chance in Small Populations
Genetic drift: process by which chance events change allele frequencies.
Population Size Matters: in a small population, a particular allele may be carried by only a few organisms. In a large population, chance events are unlikely to significantly alter its genetic composition because random removal of a few individuals´alleles won't have a big impact on allele frequencies in population as a whole.
A population bottleneck can cause genetic drift: in a population bottleneck, population Is so drastically reduced by a natural catastrophe or overhunting. After this, only few individuals are available to contribute genes to next generations.
Isolated founding populations may produce bottlenecks: founder effect occurs when isolated colonies are founded by small numbers of organisms.
Mating Within a Population is Almost Never Random
Sexual reproduction between relatives is called inbreeding. Tends to increase the number of individuals that inherit the same alleles from both parents and are therefore homozygous for many genes. This can have harmful effects.
Assortative mating: preference for mates that are similar.
Neither inbreeding or assortative mating by themselves will alter allele frequencies in a populations but they can have large effects on the distribution of genotypes and phenotypes.
All Genotypes Are Not Equally Beneficial
In equilibrium population no genotype has any advantage over the others.
Natural selection: process in which individuals with traits that help them survive and reproduce leave more offspring than do individuals that lack those traits.
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